Therapeutic Drug Monitoring in Psychiatry: Experience from Norway

In recent years therapeutic drug monitoring (TDM) has become more widely used in Norway, although TDM has been available for several decades. Department of Psychopharmacology in Oslo experienced a 10-fold increase in the number of serum samples received for analysis from 2001 to 2003. Other laboratories in Norway have also experienced large increases, and it is estimated that a total of approximately 150 000 serum analyses of psychoactive drugs were performed in Norway in 2003.

Serum analysis is available in Norway for most of the commonly used psychoactive drugs. Increased use of TDM is seen both in therapy with antidepressants and antipsychotics as well as antiepileptic drugs used as mood stabilizers. Although more psychoactive drugs are being marketed and prescribed, the large increase in serum analyses performed in Norway cannot be explained by increased drug consumption. During recent years, however, there has been an increased awareness of TDM as a helpful tool for evaluating effects and quality control of drug treatment in psychiatry. Furthermore, increased awareness of the great variability in individual therapeutic response and occurrence of side effects as well as the problems of compliance in psychiatry and drug interactions, are all reasons for increased use of TDM.

Cost-benefit analyses of TDM in psychiatry, however, are scarce. Measurement of the serum concentration of a drug by itself may be of little clinical value. The clinical value of TDM relies on the interpretation of the result. Focus on the quality of a report provided together with the result of the serum analysis is assumed to be a major explanation for the 10-fold increase in serum analyses during the last three years in Oslo.